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Write to measurement file note: x values only guaranteed for one data signal?

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Hi everyone,

 

Attached is a vi I have developed... When I save the data my .lvm file has a note in the header than says" X values only guaranteed for Power (Filtered)".... Power is one of 9 signals... I am not sure what this note means, but I assume that there is a problem synching these signals to a common timebase...

 

Would someone be able to explain this note and how I can fix it? Any comments/advice would be greatly appreciated.

 

Regards,

Jack

 

 

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Since you are acquiring all of the signals with one DAQ Assistant, you are using a shared timebase for the acquisition. However, by converting some of the signals to scalars with the formula node, those signals have no t0 or dt infomation anymore.

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Hi Dennis,

 

Thanks for your reply... How can I change the scalars to dynamic data?... I want this single value to be written as the same rates of the other values (4kHz).... So the current heart rate value should be written each iteration as with the other data until the value updates...? That is to say, I want a heart rate value for every data point/row in the .lvm file?

 

Any suggestions would be appreciated... I have been working on this for some time and am getting no where..

 

Regards,

Jack

 

 

 

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Solution
Accepted by topic author jcannon
Everything IS being written to the file at the same rate. If you want a whole lot of duplicates, you would need to build an array the same size as the raw data.
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Thanks Dennis... I used the initialize array function to provide duplicate data points the same size as the samples to readeach loop iteration ...

 

On that note, what is the best number of samples to read when acquiring data in a while loop?... Typically, I set it to be 10% of the sample rate... So in this instance, I have a sample rate of 2kHz and read 200 samples per iteration...

 

Would you have any comments on this?

 

Thanks and regards,

Jack

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Hello Jack, 

 

Reading at 10% of your sample rate is what is typically advised. This is shown here under the section From Hardware Buffer to Software Buffer.. 

 

Regards,

 

Izzy O. 

Applications Engineer

National Instruments

 

 

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Hi Izzy,

 

Thanks for the reply... I had not previously seen that document... Helps alot..

 

Regards,

Jack

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